This invention relates to an improved tubing hanger with a provision which allows preloading of the connection of the tubing hanger to the wellhead housing to overcome certain disadvantages of prior subsea tubing hangers.
Tubing hangers are typically designed to support the weight of the associated tubing strings by landing on a seat within the wellhead housing. This seat may be a reduced diameter surface machined on the interior of the wellhead housing or a similar surface on a packoff or casing hanger previously installed in the wellhead housing. The tubing hanger is then secured in this position by urging a split ring carried on the tubing hanger body into a recess in the wellhead housing interior wall which prevents upward movement of the tubing hanger. Due to manufacturing tolerances and debris which may have accumulated on the landing seat in the wellhead housing during prior drilling operations, it has been necessary to make the recess which the split ring engages longer than the split ring. This additional length allows room for the tubing hanger and split ring to reciprocate within the recess as the tubing string lengths grow or contract due to thermal stresses. This reciprocating movement of the tubing hanger is detrimental to the seals installed on the nose of the tubing hanger.
These tubing hangers are typically installed using a running tool which allows manipulation of the tubing hanger and often includes hydraulically operated apparatus for installing and testing the tubing hanger before oil and gas production is commenced. Once the running tool is removed from the tubing hanger and wellhead, residual torsional force exerted on the tubing hanger by the tubing strings suspended below can cause the tubing hanger to rotate with respect to the wellhead housing and move from its original orientation. This loss of orientation can cause damage to the running tool or make it impossible to reinstall the running tool during subsequent tubing string operations. Similarly, a loss of orientation can make it unfeasible to install the subsea tree on the well thereby making it impossible to commence oil or gas production from the well. As drilling and production technology has allowed such operations in deeper water depths, operators have insisted on the use of metal-to-metal seals to seal the annulus between the tubing strings and the last casing string. These metal-to-metal seals are easily damaged by excessive movement after energization. The reciprocating and rotational motions described above are extremely deleterious to these metal-to-metal seals. The present invention overcomes these problems by providing a novel apparatus for preloading the tubing hanger after installation to prevent reciprocating or rotational movement of the tubing hanger and its seals.
U. S. Pat. No. 3,693,7I4 to B. F. Baugh discloses a typical prior art tubing hanger and running tool which utilizes an expansible lock ring to secure the tubing against upward movement with respect to the wellhead housing.
U. S. Pat. No. 4,067,062 to B. F. Baugh is an example of a tubing hanger allowing use of multiple tubing strings and an associated hydraulic running tool which can run and lock the tubing hanger within the wellhead and is releasable therefrom. The running tool can be subsequently reconnected to the tubing hanger and hydraulically unlatch the tubing hanger and retrieve it to the surface.
U. S. Pat. No. 4,067,388 to E. M. Mouret discloses a running tool and tubing hanger combination which allows release of the tool from the tubing hanger by hydraulic pressure or rotation of the running string to which the tool is attached.
U. S. Pat. No. 5,145,006 to D. R. June discloses a novel running tool and tubing hanger combination which allows preloading of the tubing hanger to wellhead housing connection. This invention utilizes an extendible ring which is operated by the running tool to preload the tubing hanger to wellhead housing connection.